Conventionally, such a gate valve for high vacuum use generally comprises a valve housing, and a valve body mounted thereto adapted to open and close the valve opening formed in the valve housing. The valve body comprises a valve plate and a counter plate arranged opposite to each other, and the valve plate is adapted to close the valve opening by being urged against the valve seat formed in the valve housing. In a gate valve of this kind, in order to urge the valve body against the valve seat to perform a sealing action thereto, mechanism such as those using a linkage, a shifting mechanism with taper blocks, or a mechanism utilizing balls or rollers, etc. have been used.
However, it has been well-known that these mechanisms reveal various problems in that they all have members such as rolling members, shifting members, etc., which move relative to each other, so that during the use of the gate valve in a highly vacuum atmosphere the relatively moving members may become clogged, making the opening or closing of the valve body impossible, its rapid opening or closing impossible, or dust may be generated due to the relative movements of the members, etc.
In order to solve these problems to some extent, gate valves have already been proposed in which as a sealing mechanism a metallic bellow, diaphragms, etc. are used, and two types of these valves are known, i.e. one in which double bellows are arranged concentrically on the valve seat confronting the valve plate, the other in which a metallic bellows is arranged between the valve plate and the counter plate. Among these types, in the former, since the bellows is arranged at the side of the valve seat it has a complicated constitution, and is thicker and excessively heavy in comparison with the latter type. On the other hand, the latter type has such defects that, since the weight of the valve plate portion is great owing to the arrangement of the metallic bellows, a guide mechanism for preventing the valve plate from oscillations, etc., the relatively sliding portions need to be provided within a high vacuum environment.
Thus, it will be apparent that in these proposed gate valves for high vacuum use there are also various problems in their constitution.
As a gate valve for high vacuum use, the present applicant has already proposed an invention entitled "A Non-Sliding Gate Valve for High Vacuum Use" as Japanese Patent Application No. 62-86937, filed on Apr. 10, 1987, for the purpose of resolving the problems inherent to hitherto known gate valves.
As apparent from the Specification and drawings of the above previously proposed patent application, this "non-sliding gate valve for high vacuum use" has the following constitution as shown in FIGS. 2 and 3 of the appended drawings.
The gate valve comprises a hollow box-like valve housing 1 having substantially an elliptical configuration when viewed in an elevational view and of a shallow depth when viewed from the side, and a valve body 2 disposed therein and having substantially a circular plate-like shape, the valve body 2 being adapted to close or open the valve opening 1.sub.1 formed axially in the valve housing 1. On the outside of the valve housing 1, on its top wall 3 a pair of brackets 4.sub.1 , 4.sub.2 are vertically secured thereto with a gap being left therebetween in the longitudinal direction of the top wall 3 (see FIG. 3), a bearing member 5 having substantially an inverted U-shaped configuration being disposed within the gap between the brackets 4.sub.1 and 4.sub.2 with its leg members 5.sub.1 and 5.sub.2 being pivoted to the confronting brackets 4.sub.1 and 4.sub.2, respectively, by pivot 6.sub.1 and 6.sub.2, respectively. The central web portion 5.sub.3 of the bearing member 5 has a hollow bar-like rod 7 centrally secured near its upper end portion, the valve body 2 being radially secured to the rod 7 at its lower end. Swingably secured on the outside of the valve housing 1 is an air cylinder 8 at its piston rod end so that its center line orthogonally intersects the longitudinal axis of the valve housing 1 (see FIGS. 2), whereby the end of the piston rod of the air cylinder 8 is swingably connected to the rod 7 near its upper end portion and above the bearing member 5 having an inverted U-shaped configuration. Thus, by actuating the air cylinder 8 to extend or retract the piston rod, the rod 7 is swung together with the bearing member 5 secured thereto about the pivots 6.sub.1, 6.sub.2 relative to the brackets 4.sub.1, 4.sub.2 secured to the valve housing 1. Therefore, the valve body 2 secured to the rod 7 at its lower end portion can be selectively swung to a position indicated at the solid lines in FIG. 2 where it closes the valve opening 1.sub.1, or to a position indicated at the phantom lines in FIGS. 2 where it opens the valve opening 1.sub.1.
As shown in FIG. 3 the valve body 2 comprises a valve plate 10, a counter plate 11, both arranged in line with the center line of the valve opening 1.sub.1, and a metallic bellows 13 sealingly connecting the valve plate 10 and the counter plate 11 at their opposing outer peripheries. The valve plate 10 and the counter plate 11 are respectively made of a circular metallic plate of substantially identical dimensions, and respectively constituted from a pressure-resisting metallic concave dish-like plate 14, 15, a sealed space 16 being defined by the valve plate 10, counter plate 11, and metallic bellows 13, and is adapted such that, when pressurized air is supplied to it from the outside through a passage 7.sub.0 formed in the rod 7 to which the valve valve body 2 is secured at its upper portion, the metallic bellows 13 is urged to expand against its elasticity so that the valve plate 10 and the counter plate 11 are respectively urged against the valve seat 17 formed around the valve opening 1.sub.1 and against the wall 18 formed within the valve housing 1 opposite the valve opening 1.sub.1 which constitutes a counter plate receiving seat for the counter plate 1.sub.1, thereby the counter plate 11 acting to assist the valve plate 10 being strongly urged against the valve seat 17 to sealingly close the valve opening 1.sub.1. Inversely, in order to open the valve opening 1.sub.1 from this closed state, upon discharge of the pressurized fluid from the sealed space 16, the bellows 13 contracts due to its elasticity, resulting in the separation of the valve plate 10 from the valve seat 17, and, in this case, the separation of the counter plate 11 from the counter plate receiving seat 18 is assisted by the action of a compressive coil spring (not shown) disposed outside the valve housing 1.